- estimate, for it includes only the energy radiated into the air.
The actual amount of energy released in the form of α rays is evidently much greater than this on account of the absorption of the α rays by the active matter itself.
It will be shown later that the heating effect of radium and of its products is a measure of the energy of the expelled α particles.
244. Heat emission of radium. P. Curie and Laborde[1]
first drew attention to the striking result that a radium compound
kept itself continuously at a temperature several degrees higher
than that of the surrounding atmosphere. Thus the energy
emitted from radium can be demonstrated by its direct heating
effect, as well as by photographic and electric means. Curie
and Laborde determined the rate of the emission of heat in
two different ways. In one method the difference of temperature
was observed by means of an iron-constantine thermo-couple
between a tube containing one gram of radiferous chloride
of barium, of activity about 1/6 of pure radium, and an exactly
similar tube containing one gram of pure barium chloride.
The difference of temperature observed was 1·5° C. In order to
measure the rate of emission of heat, a coil of wire of known
resistance was placed in the pure barium chloride, and the
strength of the electric current required to raise the barium to
the same temperature as the radiferous barium was observed. In
the other method, the active barium, enclosed in a glass tube, was
placed inside a Bunsen calorimeter. Before the radium was introduced,
it was observed that the level of the mercury in the stem
remained steady. As soon as the radium, which had previously
been cooled in melting ice, was placed in the calorimeter, the
mercury column began to move at a regular rate. If the radium
tube was removed, the movement of the mercury ceased. It was
found from these experiments that the heat emission from the
1 gram of radiferous barium, containing about 1/6 of its weight of
pure radium chloride, was 14 gram-calories per hour. Measurements
were also made with 0·08 gram of pure radium chloride.
Curie and Laborde deduced from these results that 1 gram of pure
radium emits a quantity of heat equal to about 100 gram-calories
per hour. This result was confirmed by the experiments of Runge
- ↑ P. Curie and Laborde, C. R. 136, p. 673, 1903.
